1 files changed, 65 insertions, 51 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index a09e077ba925..2a930a752a78 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -236,10 +236,7 @@ __u16 GetNextMid(struct TCP_Server_Info *server)
 {
         __u16 mid = 0;
         __u16 last_mid;
-        int   collision;
-
-        if (server == NULL)
-                return mid;
+        bool collision;
 
         spin_lock(&GlobalMid_Lock);
         last_mid = server->CurrentMid; /* we do not want to loop forever */
@@ -252,24 +249,38 @@ __u16 GetNextMid(struct TCP_Server_Info *server)
         (and it would also have to have been a request that
          did not time out) */
         while (server->CurrentMid != last_mid) {
-                struct list_head *tmp;
                 struct mid_q_entry *mid_entry;
+                unsigned int num_mids;
 
-                collision = 0;
+                collision = false;
                 if (server->CurrentMid == 0)
                         server->CurrentMid++;
 
-                list_for_each(tmp, &server->pending_mid_q) {
-                        mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
-
-                        if ((mid_entry->mid == server->CurrentMid) &&
-                            (mid_entry->midState == MID_REQUEST_SUBMITTED)) {
+                num_mids = 0;
+                list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) {
+                        ++num_mids;
+                        if (mid_entry->mid == server->CurrentMid &&
+                            mid_entry->midState == MID_REQUEST_SUBMITTED) {
                                 /* This mid is in use, try a different one */
-                                collision = 1;
+                                collision = true;
                                 break;
                         }
                 }
-                if (collision == 0) {
+
+                /*
+                 * if we have more than 32k mids in the list, then something
+                 * is very wrong. Possibly a local user is trying to DoS the
+                 * box by issuing long-running calls and SIGKILL'ing them. If
+                 * we get to 2^16 mids then we're in big trouble as this
+                 * function could loop forever.
+                 *
+                 * Go ahead and assign out the mid in this situation, but force
+                 * an eventual reconnect to clean out the pending_mid_q.
+                 */
+                if (num_mids > 32768)
+                        server->tcpStatus = CifsNeedReconnect;
+
+                if (!collision) {
                         mid = server->CurrentMid;
                         break;
                 }
@@ -381,29 +392,31 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
 }
 
 static int
-checkSMBhdr(struct smb_hdr *smb, __u16 mid)
+check_smb_hdr(struct smb_hdr *smb, __u16 mid)
 {
-        /* Make sure that this really is an SMB, that it is a response,
-           and that the message ids match */
-        if ((*(__le32 *) smb->Protocol == cpu_to_le32(0x424d53ff)) &&
-                (mid == smb->Mid)) {
-                if (smb->Flags & SMBFLG_RESPONSE)
-                        return 0;
-                else {
-                /* only one valid case where server sends us request */
-                        if (smb->Command == SMB_COM_LOCKING_ANDX)
-                                return 0;
-                        else
-                                cERROR(1, "Received Request not response");
-                }
-        } else { /* bad signature or mid */
-                if (*(__le32 *) smb->Protocol != cpu_to_le32(0x424d53ff))
-                        cERROR(1, "Bad protocol string signature header %x",
-                                *(unsigned int *) smb->Protocol);
-                if (mid != smb->Mid)
-                        cERROR(1, "Mids do not match");
+        /* does it have the right SMB "signature" ? */
+        if (*(__le32 *) smb->Protocol != cpu_to_le32(0x424d53ff)) {
+                cERROR(1, "Bad protocol string signature header 0x%x",
+                        *(unsigned int *)smb->Protocol);
+                return 1;
+        }
+
+        /* Make sure that message ids match */
+        if (mid != smb->Mid) {
+                cERROR(1, "Mids do not match. received=%u expected=%u",
+                        smb->Mid, mid);
+                return 1;
         }
-        cERROR(1, "bad smb detected. The Mid=%d", smb->Mid);
+
+        /* if it's a response then accept */
+        if (smb->Flags & SMBFLG_RESPONSE)
+                return 0;
+
+        /* only one valid case where server sends us request */
+        if (smb->Command == SMB_COM_LOCKING_ANDX)
+                return 0;
+
+        cERROR(1, "Server sent request, not response. mid=%u", smb->Mid);
         return 1;
 }
 
@@ -448,7 +461,7 @@ checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length)
                 return 1;
         }
 
-        if (checkSMBhdr(smb, mid))
+        if (check_smb_hdr(smb, mid))
                 return 1;
         clc_len = smbCalcSize_LE(smb);
 
@@ -465,25 +478,26 @@ checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length)
                         if (((4 + len) & 0xFFFF) == (clc_len & 0xFFFF))
                                 return 0; /* bcc wrapped */
                 }
-                cFYI(1, "Calculated size %d vs length %d mismatch for mid %d",
+                cFYI(1, "Calculated size %u vs length %u mismatch for mid=%u",
                                 clc_len, 4 + len, smb->Mid);
-                /* Windows XP can return a few bytes too much, presumably
-                an illegal pad, at the end of byte range lock responses
-                so we allow for that three byte pad, as long as actual
-                received length is as long or longer than calculated length */
-                /* We have now had to extend this more, since there is a
-                case in which it needs to be bigger still to handle a
-                malformed response to transact2 findfirst from WinXP when
-                access denied is returned and thus bcc and wct are zero
-                but server says length is 0x21 bytes too long as if the server
-                forget to reset the smb rfc1001 length when it reset the
-                wct and bcc to minimum size and drop the t2 parms and data */
-                if ((4+len > clc_len) && (len <= clc_len + 512))
-                        return 0;
-                else {
-                        cERROR(1, "RFC1001 size %d bigger than SMB for Mid=%d",
+
+                if (4 + len < clc_len) {
+                        cERROR(1, "RFC1001 size %u smaller than SMB for mid=%u",
                                         len, smb->Mid);
                         return 1;
+                } else if (len > clc_len + 512) {
+                        /*
+                         * Some servers (Windows XP in particular) send more
+                         * data than the lengths in the SMB packet would
+                         * indicate on certain calls (byte range locks and
+                         * trans2 find first calls in particular). While the
+                         * client can handle such a frame by ignoring the
+                         * trailing data, we choose limit the amount of extra
+                         * data to 512 bytes.
+                         */
+                        cERROR(1, "RFC1001 size %u more than 512 bytes larger "
+                                  "than SMB for mid=%u", len, smb->Mid);
+                        return 1;
                 }
         }
         return 0;